Ch. 53 Warm-Up

1. (Review) Sketch an exponential population growth curve and a logistic population growth curve.

2. What is an ecological footprint?

3. What are ways that you can reduce your ecological footprint?

Define: Demography Semelparity Iteroparity Carrying capacity Exponential growth

curve Logistic growth curve K-selection r-selection Ecological footprint

POPULATION ECOLOGYChapter 53

• Population = group of individuals of a single species living in same general area

• Density: # individuals / area

• Dispersion: pattern of spacing between individuals

Introduction

Determining population size and density:

• Count every individual

• Random sampling

• Mark-recapture method

Patterns of Dispersal:

1. Clumped – most common; near required resource

2. Uniform – usually antagonistic interactions

3. Random – not common in nature

• Additions occur through birth, and subtractions occur through death.

• Life table : age-specific summary of the survival pattern of a population

• Represent data with a survivorship curve.

• Plot # of individuals in a cohort still alive at each age.

Demography: the study of vital statistics that affect population size

Life Table

Survivorship Curves:

• Type I curve: low death rate early in life (humans)

• Type II curve: constant death rate over lifespan (squirrels)

• Type III curve: high death rate early in life (oysters)

3 Variables:

1. Age of sexual maturation

2. How often organism reproduces

3. # offspring during each event

Note: These traits are evolutionary outcomes, not conscious decisions by organisms

Life History: traits that affect an organism’s schedule of reproduction and survival

Semelparity

• Big-bang reproduction

• Many offspring produced at once

• Individual often dies afterwards

• Less stable environments

Agave Plant

Iteroparity

• Repeated reproduction

• Few, but large offspring

• More stable environments

Lizard

Critical factors: survival rate of offspring and repeated reproduction when resources are limited

N/t = B-D

N = population size

t = time

Change in Population Size

Change in population size

during time interval

Births during time interval

Deaths during time interval= -

• Zero population growth: B = D

• Exponential population growth: ideal conditions, population grows rapidly

• Unlimited resources are rare

• Logistic model: incorporates carrying capacity (K)

• K = maximum stable population which can be sustained by environment

• dN/dt = rmax((K-N)/K)

• S-shaped curve

Laboratory Populations

Factors that limit population growth:

• Density-Dependent factors: population matters

• i.e. Predation, disease, competition, territoriality, waste accumulation, physiological factors

• Density-Independent factors: population not a factor

• i.e. Natural disasters: fire, flood, weather

• K-selection: pop. close to carrying capacity

• r-selection: maximize reproductive success

K-selection r-selection

Live around K Exponential growth

High prenatal care Little or no care

Low birth numbers High birth numbers

Good survival of young Poor survival of young

Density-dependent Density independent

ie. Humans ie. cockroaches

• Populations fluctuate due to biotic and abiotic factors

1975-1980: peak in wolf numbers1995: harsh winter weather (deep snow)

What do you notice about the population cycles of the showshoe hare and lynx?

Boom-and-bust cycles

• Predator-prey interactions

• Eg. lynx and snowshoe hare on 10-year cycle

Human Population Growth

• 2 configurations for a stable human population (zero population growth):

A. High birth / high death

B. Low birth / low death

• Demographic transition: occurs when population goes from A B

Age-Structure Diagrams

Global Carrying Capacity

• UN predicts: 7.8 to 10.8 billion people by the year 2050

• 2012 = 7 billion

• Estimated carrying capacity = 10-15 billion?

• Ecological footprint: total land + water area needed for all the resources a person consumes in a pop.

• 1.7 hectares (ha)/person is sustainable

• U.S.: 10 ha/person over K??

Limitations? Consequences? Solutions?

Map of ecological footprint of countries in the world (proportional sizes shown)